linux-kernel - Re: [PATCH] prctl: allow prctl_set_mm_exe

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Message-Id: <27F75C31-4DCF-42E2-AB91-948F1A5615B2@icloud.com>
Date: Wed, 28 Aug 2024 08:48:24 -0700
From: tblodt@...oud.com
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org,
 Ryan Houdek <sonicadvance1@...il.com>,
 "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
 "Eric W. Biederman" <ebiederm@...ssion.com>,
 Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] prctl: allow prctl_set_mm_exe_file without unmapping old
 exe

> Interestingly, the man page states:
> 
> "You can even type /proc/pid/exe to run another copy of the same executable that is being run by process pid."
> 
> Is that still true (with that binfmt_misc magic) once we change /proc/self/exe? Or does it with changing /proc/self/exe to point at the non-emulator exe even work as expected regarding this documentation?

This is actually one of the reasons for an emulator to want to update /proc/self/exe. If it points to the interpreter, running /proc/pid/exe starts a copy of the emulator, but without any idea of what program it was supposed to be running. If it points to the emulated program, running /proc/pid/exe will still start the emulator because it's registered in binfmt_misc, but with the emulated program. The intended result is for references to /proc/self/exe to function the same way they would without the emulator.

~Theodore